Low density container for liquids



g- 2, 1965 1.. D. BRUGH, JR 3,263,891

LOW DENSITY CONTAINER FOR LIQUIDS Filed March 25, 1964 2 Sheets-Sheet 1INVENTOR.

LATANE E BRUQH ATTORNEY 2, 1966 L. D. BRUGH, JR 3,263,891

LOW DENSITY CONTAINER FOR LIQUIDS Filed maro h 25, 1964 I 2 sheets sheet2 k k A v :2 -#-$4 m 1 FIG 2 m soooog E W i m I Z I i zsooog I i a a a a5600- a i a m mo :50 290 250 30a 350i 400 Msas waaem' man-- INVENTOR.LATANE D. BRUGH ATTORNEY United States Patent 3,263,891 LOW DENSITYCONTAINER FOR LIQUIDS Latane I). Brugh, Jr., Rte. 1, Covington, Va.Filed Mar. 25, 1964, Ser. No. 354,551 7 Claims. (Cl. 2293.1)

The present invention pertains to a novel container of the type used forpackaging of liquids.

At present, a large portion of the containers used in packaging liquidsare formed of a stiff paper, generally referred to as paperboard orsimply, board, with a moisture resistant coating. In the packaging ofmilk, for example, this type of container has, to a large extent,supplemented other types of containers, such as glass bottles.

In forming paper, liquid containers, certain criteria have heretoforedictated the use of a paper stock of relatively high basis weight anddensity; the term basis weight, as used herein, referring to the weightper 3,000 square feet of board, while the term density is expressed asthe ratio of basis weight to caliper or thickness measured inthousandths of an inch.

Thus, since economic considerations require that the cartons be filledand sealed on high-speed, automatic packaging machinery and because ofthis, the cartons must possess a certain amount of stiffness, a fairlyheavy, dense board has generally been felt necessary. Similarly, inhandling and storage of the cartons subsequent to filling .and sealing,the necessity of rigidity and resistance to bulge has led the industryto require a paper stock of relatively high basis weight.

An additional consideration, which to a great extent has limited thetype of paper stock usable in liquid containers, is the adaptability ofthe stock to coating with a moisture-proof material. For example, if thesurface of the board is fairly rough or uneven, with fibers, or groupsof fibers, extending away from the general surface of the board, thecoating will be thin in some spots with many of the fibers and fibergroups extending through the coating.

This will usually result in an unacceptable carton since the thin spotsare possible sources of subsequent carton failure and thediscontinuities in the coating caused by protruding fibers provide pathsfor moisture to travel into the board.

In prior art cartons, this roughness has been overcome by passing thecarton stock through a plurality of calender stacks; thereby forming adense, smooth surfaced board. Of course, in producing this type ofboard, the cost will necessarily be 'higher than in the production ofless dense board of comparable thickness since the fiber content will beproportionately greater.

Another manner in which unevenness of the board might be compensated forwould be to increase the thickness of the moisture-proof coating to apoint where all fibers were completely covered. However, since the costof the coating material is relatively high, this approach,

for the most part, is impractical.

Closely related to these considerations is another which results fromthe construction of the cartons generally used in this type ofpackaging. Thus, in the formation of paper, liquid containers, alongitudinal seam is generally formed as a lap joint running the lengthof the carton; resulting in severed uncoated edge of a carton blankbeing placed on the inside of the carton in contact with the liquidproduct. Because of this, it had previously been thought that acomparatively high density board must be used to prevent absorption bythis edge, or wicking, as it is referred to by those skilled in the art.

Therefore, for reasons of stiffness, good coatability andnon-absorption, paper, liquid containers have, as noted supra, beenheretofore formed from a fairly heavy, dense board. For example, in theconstruction of half- 7 3,263,891 Patented August 2, 1966 "ice galloncontainers, a stock having a basis weight of approximately 286 poundsand a density, or ratio of basis weight to thickness, of 13 is mostcommonly used. With smaller cartons, such as quarts, while the samedensity is used, a thinner, lighter stock of 208 pounds per 3,000 squarefeet has been found acceptable.

While stock of this type, suitably coated with a moist-ure resistantcovering such as polyethylene, provides a satisfactory carton, it wouldbe, of course, desirable to reduce the basis weight of the containerstock, and hence, its cost, if the characteristics of stiffness,smoothness and non-absorption present in more expensive container stockcould be retained.

The present invention achieves these requirements and permits theconstruction of cartons having the desired stiffness, smoothness, andnon-absorption of prior art cartons but with paperboard of much lighterweight, and hence, appreciably lower cost.

In achieving these results, applicant found that if the thickness of thestock used for the cartons was increased, the basis weight could begreatly reduced and the stiffness of the carton board retained or evenslightly increased.

While this lighter, lower density board exhibited a rough or flulfed upsurface, unsuitable as a coating base, it was found that if it wassubjected to a limited amount of heat and pressure after formation,little change in the overall caliper or density and hence, stiffnessresulted, but the surface so treated took on a smoothness heretoforefound only in denser, more compact stock. Thus, a well-formed continuouscoating comparable to that found on heavier more expensive cartons isattained with no increase in coat weight.

It was further discovered that, contrary to expected results, wicking orabsorption by the uncoated raw edge of the uncompacted board forming thecarton remained about the same as in cartons formed of denser, heavierboard.

These, and other advantages and features of the carton of the presentinvention will become apparent from the following description andaccompanying drawings where- FIGURE 1 is a crosssectional, comparisonview through a carton wall of the prior .art and .a carton wallaccording to the present invention;

FIGURE 2 is a somewhat schematic representation of the manner in whichthe surface of the stock forming the carton of the present invention issmoothed;

FIGURE 3 is a graphical representation of the effect on stiffness causedby varying the basis weights of different caliper boards;

FIGURE 4 is a perspective view, with portions broken away, of aliquid-proof container; and

FIGURE 5 is a cross-sectional view taken on line 5--5 of FIGURE 4.

Turning to FIGURE 1 of the drawings, there is therein shown by way ofcontrast, a cross-sectional view through a wall of a carton of the priorart and a similar view of a wall of a carton of the present invention.From this figure it will be noted, that although paperboard core 11 ofthe prior art and core 12 of the present invention are both coated withpolyethylene or a similar moistureproof coating 13, board 12 is lessdense but appreciably thicker. 'This results from the fact thatapplicant has found that while the stiffness and endurance of a cartonare to some extent governed by the density or weight of the board, amore significant factor is its caliper or thickness. Thus, consideringthat the stiffness of a homogenous body of material is proportional toits modulus of elasticity times its moment of inertia, and its moment ofinertia is proportional to the cube of its thickness, it becomesapparent that if these relationships hold true for a body of paperboard,varying the thickness or .3 caliper of the board will have a much morepronounced effect than varying the density alone. For example, doublingthe size or thickness would result in an increase in stiffness 8 timesthe original. It was determined, 'however, that in increasing thecaliper or thickness of paperboard While decreasing its density theinternal bonding of the fibers was slightly decreased. This resulted ina decrease of the modulus of elasticity, and to some extent, offset thegain in stiffness and endurance achieved by increasing the caliper.Thus, for paperboard a more exact definition in a case where the caliperis increased while density is decreased was found to be:

where S=stiffness, c=caliper in thousandths of an inch, d=density orbasis weight divided by caliper and K is a constant which varies withthe physical'properties of different boards. Or, since where W=basisweight,

It will, therefore, be seen that contrary to previous thoughts that afairly dense board was necessary to obtain the required stiffness andendurance, the density of the board can be decreased appreciably if thecaliper is slightly increased. Or stated somewhat differently, a boardhaving a much lower basis weight and hence cost can be used if thecaliper is increased and comparable bulge and endurance characteristicswill be obtained.

This is illustrated graphically in FIGURE 3 wherein curves are plottedfor the equation S=KW c for boards of constant calipers of 27 and 22thousandths of an inch or points and varying basis weights. These twocalipers are chosen for purposes of comparison since the formerrepresents the caliper found satisfactory by applicant for his cartonand the latter represents a common thickness of conventional cartons.

From this graph it will be noted that curve A, which represents a boardhaving a caliper of 27 thousandths of an inch, rapidly increases instiffness with small increases in basis weight. Curve B, on the otherhand, increases much more slowly. The comparison of the curves canprobably best be made by drawing a straight 'line parallel to the basisweight axis, which would represent a line of equal stiffness. If thisline is drawn through curve B at a basis weight of 286 pounds, acommonly used weight for 22 point board, the point of intersection ofthis' line with curve A will represent the theoretical weight of 27point board necessary to obtain the same stiffness. Thus, in FIGURE 3,line C represents a line of equal stiffness intersecting curve B atW=286 pounds. Considering next, the point where line C intersects curveA, it will be seen that whereas a basis weight of 286 pounds is' neededto obtain the required stiffness with 22 point board, a basis weight ofless than 202 .pounds is theoretically needed for the same stiffness ina 27 point board.

Taking into account such factors as stock formation and surfacesmoothness, and allowing a generous factor of safety, applicant hasfound that, for half-gallon cartons, a container stock of 253 pounds per3,000 square feet and a caliper of 27 thousandths of an inch issatisfactory; while for smaller sizes, such as quarts, stock havingabasis weight of 184 pounds per 3,000 square feet and a thickness of19.5 thousandths of an inch is more than adequate. In either case, itwill be noted that the resulting density is less than 10 pounds perpoint.

In comparative tests made between cartonsconstructed according to thepresent invention and conventional cartons, the less expensivecontainers of the present invention proved at least comparable, and inmost instances, superior to those formed of heavier, denser board. Inthe tests set forth below, cartons formed of stock having a basis weightof 286 pounds per 3,000 square feet, a caliper of 22 thousandths of aninch or 22 points and a density of 13 pounds per point were comparedwith cartons constructed according to the present invention of a stockhaving a basis Weight of 253 pounds per 3,000 square feet, a caliper of27 thousandths of an inch or 27 points and a density of approximately9.3 pounds per point. In the tabulations below the latter are referredto as L.D. cartons and the former, H.D. In all other re spects, thecartons were, as nearly as possible, identical.

The tests conducted are standard tests generally refered to as the45-minute shake test, the 7-day bulge test, and the %-ll10h drop test.

In the 45-minute shake test, filled, sealed cartons are packed inall-wire, 4 /z-gallon case and placed on a mechanical shake table; Thetable is then shaken with one inch strokes at 210 cycles per minute for45 minutes; the cartons being rotated each 15 minutes. At the end of 45minutes, the cartons are checked for leakers and the results expressedas the percentage of good or non-leaking cartons remaining. The resultsof this test were as follows:

Number Number 0t of Number Percent Carton Cartons Leakers Good GoodTested H.D 18 7 11 61 L.D 1s 0 is In the 7-day bulge test the cartonsare filled to their nominal capacity and their maximum dimension fromfront to back and side to side measured and totaled. The cartons arethen stored for seven days at 45 F. and their maximum front to back andside to side dimensions again measured and totaled. The firstmeasurement is then subtracted from that made after seven days and theresult expressed as the total bulge occurring in the sevenday storageperiod. The average results of this test were as follows:

Carton Total bluge, inches H.D .05

The A-inch' drop test consists in dropping a filled, sealed carton inchonto a flat surface, 35 times a day. After each days drops, the cartonisstored for one day at 40 F., after which it is placed under a 50%relative humidity for a one hour sweating period prior to commencingdrop testing. This procedure is continued until leakage of the carton isdetected and the result expressed as either the number of days or thenumber of drops to In summary, it Will be noted that the cartons of thepresent invention, although formed from stock 33 pounds lighter in basisweight than the comparison cartons, exhibited a total bulge after sevendays only one onehundredth of an inch greater, while in endurance teststhey proved superior. Since basis weight, as a single fact-or, isprobably the most effective in determining carton costs, the savings informing cartons of stock 33 pounds per 3,000 square feet lighter areobvious.

Thus, it will be seen that applicant has succeeded in producing a cartonhaving endurance and bulge characte-ristics equal to cartons using muchheavier and more expensive carton stock with a lower weight, and hence,cheaper paperboard. I

While endurance and bulge are primary considerations in the formation ofpapenboard liquid containers, yet another factor must be consideredwhich would seem to indicate that low density paperboard is unsuitablefor this purpose. Thus, while applicant found that, with regard tostiffness, cartons formed of lighter, cheaper board performed as well orbetter than conventional cartons if the caliper of the carton stock wasincreased, the rougher surface characteristic of the low density boardresulted in coating discontinuities or pinholing when attempts were madeto cover with conventional coat weights.

For example, when using polyethylene as a coating, standard industrypractice is to apply a coat weight of approximately 18 pounds per reamon the inside of the container where intimate contact is made betweenthe container and the stored product. Since the outside of the carton isnormally not subject to the same amount of contact with moisture'as theinside, this surface need only have a coating sufficient to resistpenetration of moisture from less intensive sources, such as from icing,condensate, and the like. Therefore, a coating of approximately poundsof polyethylene per ream of board is usually suflicient for the outsideof the carton. However, even though the overall outside coat weight maybe decreased appreciably from that used on the inside, it is stillnecessary that this coating be substantially continuous. Applicantfound, however, that with the rough surfaced, low density stock, itwould be necessary to use approximately 18 pounds of polyethylene perream of board on both surfaces to decrease pinholing to an acceptablelevel. Therefore, even though the stock used in the carton of thepresent invention is much lower in cost, the higher weights of coatingnecessary to obtain a pinhole free surface would render its useimpractical since the increased use of the relatively more expensivecoating material would more than offset any savings made by using thelighter board.

Referring to FIGURE 2 of the drawings, the manner in which this problemis overcome will be described. At the left hand side of FIGURE 2 will beseen the untreated, rough surface board 12' having fibers and fibergroups, as at 14 and '15, extending away from the general plane of thesurface. As the board 12 travels toward the right, as seen in FIGURE 2,it passes between a pair of rollers 16 and 17, portions only of whichare shown, where it is subjected to heat and a fairly light pressure.

Roller 16 is heated by steam or the like and may be conveniently made ofa polished metal, such as steel, while roller 17 is formed of a fairlyhard, yet resilient material, such as hard rubber. In practice it hasbeen found that a pressure of between 400 and 500 pounds per lineal inchin the nip formed by rolls 16 and 17 and a temperature of approximately350 F. is satisfactory. As noted previously, while the heated roll 16 isconveniently formed from a relatively rigid material such as steel, roll17 should be somewhat resilient to permit its deformation at the nip.For example, a material having a plastomer index of 35 to 40 when atemperature equilibrium is reached has proven satisfactory. Thisdeformation of the roll 17 as the board passes through the nip resultsin a varying speed of the web across the nip. Since the amount offriction between the rubber roll 17 and the board is greater than thatbetween the polished metal roll 16 and the board, the speed variationacross the nip causes the board to slide against the polished roller,bufling or burnishing it, and producing the comparatively smooth surface18 seen at the right hand side of FIGURE 2.

At the same time, the resilient roll 17 also tends to smooth the surface19 of the board, although not to the extent that surface 18 is smoothedby roll 16. Of course, if it were desired to have both surfaces of theboard equally smooth, both could be treated in the same manner by, forexample, using two pairs of oppositely disposed rollers.

However, in the specific application contemplated here, i.e., liquidcontainers, this is generally unnecessary. This results because, asnoted supra, even very rough textured board can be coated fairlysatisfactorily with, for example, a polyethylene coating of 18 poundsper ream. Since, after treatment by the roller 17, the surface 19 of theboard is much smoother than before treatment, the 18 pound coating isthen more than adequate to provide a good continuous coating. Therefore,since a polyethylene coating of 18 pounds per ream is standard on theinside of conventional cartons, if the surface 6 is used as an insidecarton surface, no increase in coat weight will be necessary when usingthe lighter board. At the same time, due to the burnishing by the roller16 of the surface 18, a coating of polyethylene of 10 pounds per ream onthat surface is sufiicient to prevent pinholing. This, as noted above,is the conventional coat weight used on the outside of liquid cartons.Thus, although both surfaces may be burnished if desired, it will beseen that by burnishing only one surface of the rough textured board,increases in coating are completely avoided.

It will be apparent, therefore, :that by treating the rough surface ofthe low density board in the manner described above, both surfaces aresmooth, although to different degrees, allowing a pinhole free coatingof 18 pounds per ream to be applied to the inside of the carton and asimilarly continuous coating of only 10 pounds to the outside. It willthus be :seen that, although the weight of the board is decreasedappreciably, no increase in coat weight is necessary to obtain'thedegree of coating continuity previously obtainable only in the heavier,denser board.

Referring to FIGURE 4 of the drawings, the problem of raw edgeabsorption, or wicking, will now be considered. In FIGURE 4 is shown,for purposes of illustration, a carton 1 of fairly common configuration.In this type of carton, a one-piece blank is severed from a sheet ofstock material suitably coated with a moisture resistant coating andfolded to the configuration shown to form an upright side wall portionincluding side wall panels 25, a bottom wall 6, and a gable top 7. Whilethe carton shown for purposes of illustration exhibits four distinctside wall panels, it will be apparent that the carton may take the formof any one of several different configurations commercially available,such as that wherein the side wall portion is formed as a truncated coneand a separate insert is secured in place as a bottom wall. Regardlessof the particular configuration chosen, in most coated paper containersof this type, at least the side wall portion is formed from a singlepiece of stock and folded to form a tubular shape. The free ends of theblank are then lapped, as at 8, to form a longitudinal seam.

Referring now to FIGURE 5 of the drawings, a crosssectional view of thelap joint formed in the construction of the carton is shown in moredetail. As therein shown, the two edges 9 and 10 of the carton blank aresecured in overlapping relationship, with edge 9 overlying inwardlyfolded edge 10. Since the paperboard core is coated with a moistureresistant coating material 13, such as polyethylene, it will be apparentthat the carton is, for the most part, liquid proof. However, since thecarton blank is stamped from the sheet of stock material after coating,the edges thereof will be uncoated. This presents no problem withuncoated edge 9, since it lies outside of the carton. Edge 10, however,is in direct contact with the stored fluid, where it provides a possiblemeans for liquid to penetrate into the material of the container. Whilea slight penetration is permissible, if the liquid tends to travel intothe board or wick, delamination of the carton board will occur andcarton failure will result.

Prior to the present invention it was thought that, in order to preventsubstantial penetration through this uncoated portion, the board wouldhave to be made relatively dense, that is, on the order of 13 pounds perpoint.

Applicant has found, however, that the density of the board may bereduced materially without substantial wicking. While the reason forthis phenomenon has not yet been fully explained, one possibleexplanation is, that the suspended solids carried by many edible, liquidproducts, such as milk, are filtered out by the fibers at the raw edgeand seal off the path therethrough. Of course, the surface tension ofthe liquids may also have an inhibiting effect on the natural tendencythereof to migrate through the minute interstices of the cartonmaterial. However, regardless of the reason, applicant has found thatwith cartons formed of board having a density of less than 10 and usedfor the storage of milk, for example, penetration through the raw edge,or wicking, is negligible as in cartons formed of heavier, denser stock.

It will be seen, therefore, that although the basis weight and density,and hence, the cost of the board are decreased by increasing thethickness of the board while decreasing the fiber content, raw edgeabsorption remains negligible, as in heavier, high density boards.

From the foregoing it will be apparent that applicant has devised apaperboard liquid container with characteristics of stiffness,adaptability for coating and raw edge absorption heretofore found onlyin heavier, denser, more expensive cartons but at appreciably lowercosts.

While specific details of the invention have been described above, itwill be apparent that changes may be made therein within the scope ofthe appended claims.

I claim:

1. A liquid-proof container comprising:

(a) An upright side wall portion,

(b) a bottom wall portion attached to said side wall portion at itslower edge,

(e) at least said side wall portion including a paperboard core,

(d) the ratio of the basis weight of said core in pounds per 3,000square feet to the thickness of said core in thousandths of an inchbeing appreciably less than 13, and

(e) a moisture resistant coating laminated to both sides of said core.

2. The liquid-proof container of claim 1 wherein:

(a) Said basis weight is approximately 253 pounds per 3,000 square feet,and

(b) said thickness is approximately 27 thousandths of an inch.

3. The liquid-proof container of claim 1 wherein:

(a) Said basis weight is approximately 184 pounds per 3,000 square feet,and

(b) said thickness is approximately 19.5 thousandths of an inch.

4. The liquid-proof container of claim 1 wherein:

(a) Said ratio is less than 10.

5. The liquid-proof container of claim 1 wherein:

(a) Said carton is formed from a unitary blank folded into tubular form,and

(b) longitudinal edges of said tubularly formed blank are overlappedforming a joint extending longitudinally of said carton.

6. The liquid-proof container of claim 5 wherein:

(a) Said side wall portion is formed of substantially planar side wallpanels.

7. The liquid-proof container of claim 1 wherein:

(a) The moisture-resistant coating laminated to one of said sides ofsaid core weighs approximately 18 pounds per ream of said core, and

(b) the moisture resistant coating laminated to the vother side of saidcore weighs approximately 10 pounds per ream of said core.

References Cited by the Examiner UNITED STATES PATENTS 2,327,713 8/1943Hunter 20662 3,094,432 6/ 1963 Meyer-Iagenberg 2293.1 X 3,107,83710/1963 Graser 229-3.1 3,170,568 2/1965 Carter 229-3.1 X

GEORGE O. RALSTON, Primary Examiner.

1. A LIQUID-PROOF CONTAINER COMPRISING: (A) AN UPRIGHT SIDE WALLPORTION, (B) A BOTTOM WALL PORTION ATTACHED TO SAID SIDE WALL PORTION ATITS LOWER EDGE, (C) AT LEAST SAID SIDE WALL PORTION INCLUDING APAPERBOARD CORE, (D) THE RATIO OF THE BASIS WEIGHT OF SAID CORE INPOUNDS PER 3,000 SQUARE FEET TO THE THICKNESS OF SAID CORE INTHOUSANDTHS OF AN INCH BEING APPRECIABLY LESS THAN 13, AND (E) AMOISTURE RESISTANT COATING LAMINATED TO BOTH SIDES OF SAID CORE.